Transparent solar cells let windows generate electricity

A piece of clear glass, left, is compared to a transparent solar cell, right,… (Courtesy of UCLA )

In the future, solar panels will no longer be restricted to the roof. You'll be able to put them on your windows too.

Scientists at UCLA have invented a thin, transparent solar cell that can turn the energy of the sun into electricity, while still allowing visible light to stream through it.

"If you take a piece of glass and compare it to our solar cell, it is difficult to tell the difference," said study leader Yang Yang, a professor at UCLA and director of the Nano Renewable Energy Center at California NanoSystems Institute (CNSI).

The transparent solar cell is made out of a plastic that absorbs invisible infared light while letting most visible light pass through.

Additionally, even the metal that carries the charge out of the cell is transparent. In collaboration with Paul S. Weiss, director of CNSI, Yang was able to install a silver nano wire that served as the conductive metal that is essentially invisible.

The result? A solar panel that is 70% transparent to the human eye.

There is a catch, of course: Transparent solar cells are not nearly as efficient as opaque ones. Yang said that by solving the visibility problem, 30% of a cell's energy-absorbing capability had to be sacrificed.

The good news is that the process is very economical, and the material can be fabricated as a liquid that can be sprayed on a surface, much in the same way that car factories spray paint onto automobiles.

Yang said he had already received calls from people ready to buy the transparent solar cells, but he does not expect the product to be ready for commercial use for at least five years.

"I don't have the patience to wait much longer," he said. "I'd like to say in five years we'll have something on a small scale, and then in 10 years it will be popular."